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Worm complex still concern for some

The bollworm/budworm complex caught many Missouri Bootheel cotton producers off-guard in 2002, reducing yield by an estimated 35,000 bales and costing an average $36 per acre in control. That compared to a little over 2,000 bales of damage in 2001 and an average control cost of $3.13 per acre.

That made the bollworm/budworm complex the top pest in Missouri Bootheel cotton during 2002, followed by thrips, Lygus, cotton fleahopper and aphids. In 2001, lygus was the number one pest, followed by cotton fleahopper, thrips and bollworm/budworm.

It's hard to predict how insect dynamics will play out in 2003, noted Michael Boyd, Extension entomologist at the University of Missouri's Delta Research Center in Portageville, but winter weather can provide a clue.

“A mild, dry winter usually means more insect pressure the following year,” Boyd said. “This winter has been pretty cold and wet, so I suspect that insect populations will be down somewhat.”

One pest sure to cause problems again this year is thrips, according to Boyd. “In 2002, we had a lot of cotton that was really struggling to break through the soil surface, and when it did, it sat there for a while. Those plants took on quite a bit of damage from thrips, and we had more applications for thrips than we've seen in previous years.”

This happened in fields that weren't treated with an in-furrow or seed treatment and in fields that were. In the case of the latter, “The plants just weren't taking up the insecticides like they normally would.”

By mid-season of 2002, Bootheel cotton producers were seeing scattered outbreaks of plant bugs, according to Boyd. As for 2003, “I would definitely keep an eye on them. Some of the alternate weed hosts are starting to grow, and I would say a lot of the plant bug complex has built back up.”

The past winter “was ideal in terms of killing off a lot of boll weevils,” noted Boyd. The area is under active eradication, but there is concern that weevils could migrate from non-eradicated areas (in northeast Arkansas).

The budworm/bollworm complex in 2002 was predominately populated by budworms “on the west side of the Bootheel next to the St. Francis River, based on trap counts and observation. On the east side of the river, it was more of a mixed population,” according to Boyd.

Traditionally, Missouri Bootheel cotton producers don't plant a lot of Bt cotton, “but in 2002, the percentage was up around 20 percent because the only way the producers could get the Roundup Ready technology was through the stacked gene varieties.”

That ended up being an advantage for a lot of producers who faced the biggest budworm pressure they've seen in a while, according to Boyd.

Meanwhile, non-Bt cotton took a hit from the tobacco budworm, Boyd noted. “I heard reports of growers treating five or six times for worms.”

The bollworm/budworm outbreak of 2002 might have been an anomaly. Still, Boyd believes that Bt cotton acreage will be up from last year in the region, “somewhere around 50 percent.”

One pest that hasn't been a major problem in the Bootheel is the stinkbug, noted Boyd. “They're not as bad here as they are in west Tennessee. One reason is that we don't have quite the overwintering habitat here, where in west Tennessee, they have a lot more wooded fence rows.

“But we do have a lot more corn over here, and that is certainly an important early season host for stinkbugs. It remains to be seen if stinkbugs are as big a problem for us. I believe that once we're past boll weevil eradication that the plant bug complex will still be our number one issue.”

West Tennessee cotton was largely able to withstand high numbers of tobacco budworms in 2002 because growers planted so much Bt cotton, according to Scott Stewart, cotton insect specialist at the University of Tennessee's West Tennessee Experiment Station in Jackson.

According to USDA, west Tennessee planted 85 percent of its acreage in worm-resistant varieties in 2002. The bollworm/budworm situation “was serious, and we were really lucky, unlike the Bootheel and northeast Arkansas which didn't have a lot of Bt cotton,” Stewart said. “We took some pretty significant injury to our refuge cotton.”

Many Bt cotton fields were sprayed for bollworms once, some twice and a few three times. Some of those applications might not have been necessary, according to Stewart.

“Some farmers go out with an automatic application of a pyrethroid in August with the idea that they're going to get any surviving bollworms, plant bugs or stinkbugs that still might be in the fields,” Stewart said. “I try to discourage that. I'd rather they time the application based on what they're seeing from their monitoring.”

Stewart noted that in 2002, an early, heavy population of stinkbugs prior to bloom never materialized into a full-blown infestation. Still, stinkbugs have officially become a top five pest in west Tennessee cotton.

Stewart said that a stinkbug treatment is needed when 20 percent of a certain size boll have indications of stinkbug feeding. A pyrethroid is an option when more common green stinkbugs are present and the field has escaped bollworms. Orthene or Bidrin is a good treatment option for the less common, but harder to control brown stinkbug.


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